In the papermaking drying process, it has always been important to maximize heat transfer through the dryer drum to the paper web. In recent years, this heat transfer has been enhanced by mounting a plurality of longitudinal bars circumferentially around the inner surface of the steam heated dryer drums to interrupt the condensate which otherwise tends to rim around the inner surface in a substantially uniformly thick layer which effectivelly retards heat transfer from the steam to the paper web on the dryer's outer surface. When the condensate layer is interrupted, turbulence is generated in the layer which imporves the heat transfer through the condensate layer.
Such interruption of condensate flow around the inner dryer surface is referred to as "spoiling " in the papermaking industry, and the bars mounted within the dryer to accomplish this are called spooiler bars.
Barnscheidt et al and Kraus U.S. Pat. Nos. 3,217,426 and 3,808,700, respectively, teach the use and advantages of spoiler bars and the manner in which they can be mounted within a dryer drum utilizing outwardly biased rings and screws.
Appel et al further advanced the art by teaching a unique manner of circumferentially spacing the bars to optimize the turbulence of the condensate to enhance heat transfer.
More recently, the concepts of attaching spoiler bars magnetically (U.S. Pat. No. 4,195,417); with pins disposed in smooth holes, sometimes with magnetic assistance, (U.S. Pat. No. 4,267,644); and by a combination of pins disposed in smooth holes and springs biasing the bars against the dryer wall (U.S. Pat. No. 4,282,656) have been disclosed.